On a~complete orthonormal system
    
    
  
  
  
      
      
      
        
Sbornik. Mathematics, Tome 28 (1976) no. 3, pp. 315-324
    
  
  
  
  
  
    
      
      
        
      
      
      
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              			In this paper we construct in $L_2(0,1)$ a complete orthonormal system $\{\psi_n(x)\}_{n=1}^\infty$ for which every series $\sum_{n=1}^\infty c_n\psi_n(x)$ whose coefficients satisfy the condition $\sum_{n=1}^\infty c_n^2=\infty$ diverges on a set of positive measure.
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      @article{SM_1976_28_3_a3,
     author = {B. S. Kashin},
     title = {On a~complete orthonormal system},
     journal = {Sbornik. Mathematics},
     pages = {315--324},
     publisher = {mathdoc},
     volume = {28},
     number = {3},
     year = {1976},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1976_28_3_a3/}
}
                      
                      
                    B. S. Kashin. On a~complete orthonormal system. Sbornik. Mathematics, Tome 28 (1976) no. 3, pp. 315-324. http://geodesic.mathdoc.fr/item/SM_1976_28_3_a3/
